Health benefits of Kale


Once best known as the vegetable used to decorate the salad table, kale is now widely recognized as a powerhouse food. Deliciously and distinctively flavoured when eaten either cooked of raw, the versatile kale provides both superior nutrition and an interesting taste.

What Is Kale?

Botanically, kale, cabbage, cauliflower, collard greens, spring greens, and Brussels sprouts, are all varieties of the same plant, Brassica oleracea. The vegetables all look and taste different, and they have subtle differences in their nutritional qualities too, but they can interbreed to make even more varieties of the same basic vegetable.

Like all the other strains of cabbage, kale comes in a variety of shapes, sizes, and colours. Most North Americans are familiar with the green curly leafed Scots kale, used to garnish salad bars and late-fall flower plantings. In Europe you will find black leafed Cavelo Nero, which is also known as Tuscan cabbage, Tuscan kale, black cabbage, Lacinato, and dinosaur kale. There are also plain leaf kale, spear kale (a cross between the curly and plain varieties), and rape kale, which refers to the plant's similarity to the canola or rapeseed plant. And finally, there is an extra tall variety of kale found in pastures on the Channel Islands known as cow cabbage.

What Are the Key Nutritional Benefits of Kale?

No commonly eaten vegetable has more total antioxidant power than kale. Some berries, fruits, and nuts are better sources of free radical fighters, but among the veggies that people eat every day, kale tops the list. Antioxidants fight inflammation, and the total antioxidant content of a food is a good indication of how useful it is in combating all the diseases of excessive inflammation, ranging from joint and muscle pain, to metastatic cancer.

Total Antioxidant Content of Selected Plant Foods   (mmol/100 g)

Kale 2.34
Strawberries (cultivated) 2.33
Buckwheat flour (whole grain) 1.99
Beets, red 1.98
Beans, fava 1.86
Red cabbage 1.86
Bell peppers, orange or yellow 1.85
Bell peppers, red or green 1.84
Grapes 1.45
Sesame seeds 1.21
Beans, pinto 1.14
Brussels sprouts 1.14
Oranges 1.14
Plums 1.14
Pineapples 1.04
Cherries, sweet 1.02
Dates 1.02
Lemons 1.02
Celery 0.85
Beans, soy 0.82
Papayas 0.82
Dried fruit, raisins 0.80
Potatoes, blue 0.80
Dried fruit, figs 0.76
Onions 0.69
Beans, black-eyed pea 0.65
Corn meal 0.60
Oats, steel-cut 0.60
Broccoli 0.58
Apricots, fresh 0.52
Wheat flour, whole wheat 0.49
Kaki/Sharon 0.43
Okra 0.41
Bean (mung) 0.35
Lettuce 0.34
Bulgur 0.31
Tomatoes 0.31
Almonds 0.30
Apples 0.29
Turnips 0.29
Sweet potatoes 0.24
Cashews 0.23
Cauliflower 0.23
Rye flour 0.23
Wheat flour, white 0.23
Yucca 0.22
Pears 0.20
Cassava 0.17
Eggplant (Aubergine) 0.17
Manioc 0.17
Cantaloupes 0.15
Peas, English 0.12
Cabbage 0.10
Parsnips 0.09
Fennel 0.07
Cucumbers 0.05
Carrots 0.04
Watermelon 0.04
Zucchini (Courgette) 0.02

Kale, as with other related cabbages, is a good source of the following:

  • Carotenoids: plant chemicals related to beta-carotene, which the body can convert into vitamin A as needed.
  • Glucosinolates: protect against cancer in small doses, but act as goitrogens, interfering with the thyroid's ability to absorb iodine and make thyroid hormone in high doses.
  • Indole-3-carbinol: enhances DNA repair, and mitigates the carcinogenic effects of oestrogen in tissues that are sensitive to it.
  • Sulforaphanes: these have some cancer-fighting qualities.

Kale is also a terrific source of two particular carotenoids, lutein and zeaxanthin. No vegetable is more valuable to colon health than kale, the best food source of lutein. Lutein protects against colon cancer in both men and women. If you develop colon cancer, the more lutein you consume, the more likely the tumour is to be located where the surgeon can remove it without removing a long section of your colon. If you smoke, then lutein is even more important for your colon health than if you don’t smoke. A single serving of kale provides 15,625 micrograms of lutein, more than you will get from any lutein supplement, and nearly twice as much as the second best food for lutein, turnip greens.

Kale also contains a group of “fat blockers” called bile acid sequestrants, which trap cholesterol so that it cannot be recycled from the small intestine back into the liver. The bile acid sequestrants are concentrated by steaming kale rather than eating it raw.

All of these useful chemicals can be leached out of kale if it is boiled, but remain in the vegetable when it is eaten raw or cooked by other methods. Boiling kale for 20 minutes or longer removes essentially all of these phytonutrients, but boiling it for 10 minutes or less has minimal effect. The sulforaphanes are only released when kale is chewed; kale purees don't provide them.

Some people just don't like the taste of kale and other vegetables in the Cabbage Family. This is due to the presence of a bitter plant chemical called sinigrin, which breaks down when the vegetable is roasted. Not everyone can taste sinigrin, but some people are extremely sensitive to it.

Kale achieves its maximum antioxidant content when it is torn or cut with a sharp knife. The torn leaf produces antioxidants to heal the cut. Chopping kale with a dull knife damages the cells that produce the antioxidants, and allows the sap, which contains much of the plant's potassium, to leak out.

Black kale (black or purple because of a chance mutation in a single gene, and not because of genetic modification in a lab) contains anthocyanin pigments that carry many of the same benefits of similar purple pigments in blueberries, blackberries, and plums.

What Health Issues Are Especially Responsive to Kale?

No vegetable is more valuable to colon health than kale, the best food source of lutein. The key benefit of kale for the colon is not that it provides fibre to “scrub” the colon, but rather that it provides the antioxidant lutein.

As mentioned earlier, lutein protects against colon cancer in both men and women. If you develop colon cancer, the more lutein you consume, the more likely the tumour is to be located where the surgeon can remove it without removing a long section of your colon. If you smoke, lutein is even more important for your colon health than if you don’t smoke. A single serving of kale provides 15,625 micrograms of lutein, more than you will get from any lutein supplement, and nearly twice as much as the second best food for lutein, turnip greens.

Lutein and Zeaxanthin Content of Selected Foods(Micrograms per 100 g serving)
Food Lutein Zeaxanthin Total
Beans, green, canned 616 44 660
Broccoli, cooked 2,003 23 2,226
Carrots, baby 325 23 358
Collards, cooked 7,825 266 8,091
Corn, sweet, kernel, canned 356 528 884
Cornmeal, yellow 898 457 1,355
Eggs, whole 32 23 55
Kale, boiled 15,625 173 15,798
Lettuce, cos or romaine 2,448 187 2,635
Lettuce, iceberg 282 70 352
Orange juice, from concentrate 58 80 138
Oranges, raw 93 74 187
Persimmons, Japanese 346 488 834
Spinach, boiled 6,964 179 7,043
Tangerines 121 112 243
Turnip greens, boiled 8,173 267 8,440

 

Increasing consumption of kale has also been found to be linked with lower risks of four other cancers: bladder, breast, ovary, and prostate. The isothiocyanates the body makes from the glucosinolates in kale (it not just about eating the vegetable, you have to have a healthy liver to process the anticancer chemicals in kale, too) helps prevent both first cases and recurrences of these cancers that develop in ductal tissue.

Where Does Kale Fit in the Families of Vegetables?

As mentioned earlier, kale isn't just a member of the Cabbage Family; it actually is a cabbage in a different form. Like all the other cabbages, it is more distantly related to radishes, horseradish, turnips, and many kinds of Asian greens.

What Is the Best Way to Eat Kale Raw?

If you are going to eat kale raw, it's best to choose small, tender leaves, picked from your own garden just after the first frost, or that you at least have stored for a few hours (overnight is optimal) in the coldest part of your refrigerator, but not in the freezer. Brief exposure to near-freezing temperatures brings out the natural sugars in kale and masks any bitter flavours. You can temper the flavour of kale by adding lemon juice and olive oil to the vegetable for eating by itself or for use in any salads.

In Japan, kale juice is the base for a popular health drink called Aojiru. Well, maybe popular isn't quite the right word. Many Japanese game shows feature drinking a glass of Aojiru as a punishment for failing to follow the show's rules. However, you can always add kale to sweeter vegetables like carrots, beets, or oranges, to make a healthy, if not especially palatable, drink.

What Is the Best Way to Use Kale in Salads?

Kale has a strong flavour, so it balances strong flavours. Many recipes call for kale to be combined with nuts (usually almonds or tamari-roasted almonds), or peanuts, lemon juice, and dried fruit or raisins.

What Is the Best Way to Cook Kale?

Looking for a healthy alternative to chips? Ok, cut chip-sized pieces of kale, toss with olive oil and salt, and bake in a hot oven until crispy. The green kale chips won't stand up to dipping, but can be served with a dollop of any dip you would use on potato or tortilla chips.

Mix potatoes and kale to make the traditional Irish Autumn food called colcannon. Or make an Iberian caldo verde with pureed potatoes, finely diced kale, and sausages.

Emulate African cuisine by serving kale, coconut milk, and peanuts over polenta. Or make the Swedish Christmas dish långkål, by simmering diced kale for several hours with ham or sausages, cream, salt, and pepper.

Want to make a whole meal around kale? Try this recipe for strozzapreti (Priest Stranglers).

This dish is called “priest stranglers” because of the shape of the pasta, which resembles twisted ribbons. According to an old tale, these delicious Fontina and kale dumplings got their name when a gluttonous priest ate too many of them too quickly. For maximum antioxidant power, use buckwheat pasta. Wheat pasta also works in this dish. You can substitute spinach for kale, but if you do, use ricotta instead of Fontina.

Strozzapreti (Priest Stranglers)

2 bunches of kale, stems removed and leaves cut into ribbons

1 1/2 teaspoons of dried sage or 10 sage leaves

4 cloves of garlic, peeled and smashed with the side of a knife

2 cups (300 g) finely diced peeled yellow potatoes

3/4 pound (300 g) pasta (fettuccine or tagliatelle)

5 oz (140 g) coarsely grated Fontina cheese

2 to 4 tablespoons (50 to 100 g) unsalted butter

1 teaspoon salt

Freshly grated Parmigiano-Reggiano for serving

Bring a large pot of water to boil for the pasta. While the pasta water is heating, put the onions, garlic, and sage in a saucepan with the butter until the onions are brown and the mixture has a nutty smell. Take the mixture off the heat and discard the garlic. Chop the kale.

When the pasta water reaches boiling, add the kale and one teaspoon of salt. Cook for five minutes, and then add the potatoes and cook for five or six minutes more, or until the potatoes are tender. Scoop them out, shake off excess water, and set aside in a bowl. Boil the pasta al dente, or softer, if your family prefers it that way.

Drain the pasta and add to the kale and potatoes. Season the mix with one teaspoon of salt. Finally, pour the butter and sage over the vegetables, and toss with Fontina. Serve with Parmigiano-Reggiano and freshly ground black pepper.

What Are Some Ways to Make Kale Juice More Interesting?

The thing to remember about kale juice is that “Kale likes company.” Most people find the distinctively cruciferous aroma of kale juice to be too strong. It's best to mix kale juice with something sweet or savoury, like apple, carrot, cherry, or celery juice, as this will minimize any potential bitter taste. It's actually the bitter compounds that make kale juice healthy, but no juice is healthy if people don't drink it!

How Do I Get Kids to Like Kale?

The author of this article was amazed to see little kids in Osaka lining up at a breakfast buffet and filling their plates with kale. The chef had used food colouring (natural food colouring, one hopes!) to make orange, yellow, red, and purple kale. These vibrant colours had the children piling it on their plates and greedily wolfing it down with chopsticks.

Don't have time to dye your kale? Then make sure it is a component of a salad or a main dish, but not the main feature. Add lemon, salt, and oil to reduce bitterness.

How Long Does Kale Keep?

Kale keeps longer when it is placed in a plastic bag with holes in it. The plastic keeps the rough surface of the kale from picking up bacteria from other vegetables in the produce bin. The holes in the plastic ensure that moisture does not accumulate and encourage mold. Under ideal conditions, kale keeps for about 21 days after it is harvested, but it may take up to 14 days from harvest before it actually arrives in your grocery store.

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About Andy Williams

Andy Williams has a Ph.D. in biology and a strong interest in health and nutrition. The Paleo Gut web site was created to explore the health benefits of the Paleo diet and see how it is changing lives. Also, get our free daily Paleo Gut newspaper delivered to your inbox. Please feel free to contact me and let me know about your Paleo experiences or favorite recipes.

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